1. Field of the Invention
The present invention relates to magnetoresistive materials for magnetoresistance (MR) heads, sensors or the like.
2. Description of the Related Art
Magnetoresistance sensors (hereinafter referred to as MR sensors) and magnetoresistance type heads (hereinafter referred to as MR heads) using magnetoresistive elements have been under development up to now. Permalloys of Ni.sub.0.8 Fe.sub.0.2 are primarily used for the magnetic bodies. However, the ratio of resistance change (hereinafter referred to as .DELTA.R/R) of these materials is approximately 2.5%. To obtain magnetoresistive elements having greater sensitivity, elements having a large .DELTA.R/R are required. A Ni-Co alloy film containing 60 to 80 atomic % of Ni is available as one of these elements. Even if this film is used, the value of .DELTA.R/R is approximately 5.8% at maximum.
It was discovered recently that a large magnetoresistance occurs when using a Fe/Cr, artificial superlattice film (Physical Review Letter Vol. 61, p2472, 1988). With this material, however, a large .DELTA.R/R cannot be obtained unless a magnetic field of more than 10 kOe is applied. Therefore it is difficult to put this film into practical use.
There was a report that a resistance change of about 10% as regards (when applying a magnetic field of 3 kOe) .DELTA.R/R was observed, by using an ultra-high vacuum deposition apparatus, on an artificial superlattice film composed of a Ni.sub.0.8 Fe.sub.0.2 (30.ANG.)/Cu(50.ANG.)/Co(30.ANG.)/Cu(50.ANG.).times.15 layers (Preliminary Manuscript, Applied Physical Society Meeting, Autumn, 1990). However, there are problems in that a high-cost ultra-high vacuum deposition apparatus is required to produce films and also a large .DELTA.R/R cannot be obtained unless a large magnetic field of approximately 3 kOe is applied.